1. Field of the Invention
This invention relates to wear measurement and defect detection in wheels. More particularly, this invention relates to ultrasonic testing of metallic railroad wheels or defects and excessive wear. The testing is accomplished in-track on moving wheels.
It is well known that wheel failures due to either exteme wear or defects, such as thermal cracks, are a major cause of train derailments. Therefore, it is highly desirable to sidetrack rolling stock having defective or excessively worn wheels, and to repair or replace such wheels before the tragedy of a derailment occurs.
It is also well known that tire failures in vehicles such as trucks, busses, automobiles and aircraft are a cause of serious accidents, resulting in great personal injury and property damage. Effective methods and apparatus for regularly and accurately testing tires are, therefore, also very desirable.
Prior Art
No satisfactory automated means capable of testing railroad wheels on rolling stock for wear or defects presently exists. Defective railway wheels are currently located by trained inspectors who visually check for cracks in the running surface, flange and plate sections of each wheel when it is stationary in a railway yard. Though many defective wheels are found in this manner, many more escape detection due to other equipment, such as brake shoes, journal boxes, etc., obscuring the inspector's field of view. Also small or subsurface defects are difficult for an inspector to find. Measurement of wheel wear is also performed at such times by physical placement of a gauge which measures the height of the flange above the running surface of wheel, an altogether inefficient process.
Magnetic testing of locomotive wheels has also been performed by mounting small detector coils on the locomotive in close proximity to the wheels. Small cracks, such as thermal cracks, which may develop when the locomotive is in motion disrupt the magnetic field, thereby triggering an alarm signal. This method of testing wheels is impractical because of the expense and difficulty of installing and maintaining magnetic testing apparatus at each wheel on each railway car. Furthermore, no provision for measurement of wheel wear is made in such devices.
Other currently known means of inspecting wheels more extensively all require that wheels and axle sets be removed from the railroad car for testing. These means include inspection of wheels by ultrasonic contact or by magnetic particle inspections. Although these inspection methods are quite effective, it is not feasible to regularly remove every wheel from a railroad company's entire rolling stock. Furthermore, freight trains are usually assembled at marshalling yards or division points, from cars owned by different railroad companies. It is desirable for an individual railroad company to quickly and accurately examine the wheels of such cars before including them in a train. Yet, it would be totally impractical to thoroughly check the wheels of each car by presently known methods when assembling a freight train, and visual inspection alone is too time consuming and inaccurate to suffice.
Railway cars or locomotives whose wheels are found to be defective or excessively worn are removed from service. Depending on the nature of the defect or wear, wheels or axle sets of wheels are replaced, or in some cases the vehicle is sent to a wheel truing machine to re-establish a correct wheel profile.
Similarly, no automated means for testing tires of trucks, busses, automobiles, and aircraft is currently available. Detection of defective tires is limited to visual inspection, and such inspection often does not disclose damage to the tire casing, including breaks in the reinforcing tire cord,